1. Field of the Invention
The present invention relates to a razor blade material having excellent mechanical and chemical properties, and to a razor blade made of the material. The razor blade material is characterized by that a razor blade made of the material has a cutting blade portion with high hardness, a good blade edge form accuracy, excellent sharpness, and excellent corrosion and wear resistances.
2. Brief Description of the Related Art
A conventional razor blade is made of a crystalline metal, such as carbon steel or stainless steel, which is coated with a resin. However, a carbon steel razor has problems that are lacking in enough sharpness because of extremely deteriorated hardness due to inadequate resistance to softening by tempering heat treatment, coarse carbides, and deteriorated durability due to inferior corrosion resistance.
A stainless steel razor blade has been made from, for example, a 1% C-13% Cr steel or a 0.65% C-13% Cr steel through a melting-casting process. The former can be of high hardness because of high carbon and high chromium contents, but it is liable to have an alloy structure containing coarse carbides. Therefore, in recent years, the latter of 0.65% C-13% Cr steel has been preferably used. However, while the latter contains a very small amount of coarse carbides which deteriorates the steel in corrosion resistance, it has a problem that a high hardness is not expectable because of a low carbon content.
On the other hand, the usual razor blade is coated with a resin at a temperature of 300 to 400xc2x0 C. in order to improve a shaving feel. Thus, the razor blade has a problem that a cutting edge portion of the razor blade is deteriorated in hardness down to HV600 to 650 due to heating when resin-coating the razor blade. If strength of the blade edge is inadequate, it is bent during shaving resulting in deteriorated durability. Taking this into consideration, if the carbon amount of the razor blade steel is increased in order to improve the blade edge strength so as to have high hardness, a lot of carbides (which are mainly Cr-containing carbides such as M7C3 and M23C6) each having a diameter of about not less than 0.1 xcexcm is generated, resulting in deteriorated corrosion resistance, becoming brittle and/or defects such as a break in some using manners.
Therefore, in order to produce a razor blade material from the above materials, it is necessary for those to adjust some material factors including a size and hardness by a combination of heat treatment, hot-rolling and cold-rolling resulting in increased production process steps.
In order to solve the above problems, there has been proposed a material made of an amorphous metal. Since the amorphous metal material can have remarkably improved hardness, strength and corrosion resistance, an alloy component design, which enables the alloys to become amorphous, was intensively examined in a broad range of chemical compositions at the earliest in the 1970s, as can be seen from, for example, JP-A-51-4019. There has been a trial to apply the amorphous metal for a blade material. For example, according to JP-A-54-31023, there is proposed a material being provided with an amorphous structure by adding 2 to 40 wt % of at least one nonmetal element selected from the group of P, C, B, Si, etc. to the material.
The proposed amorphous metal blade material is effective as means for improving properties of hardness, strength and corrosion resistance. However, it is required for the alloy design to be subjected to quenching solidification at least at a critical cooling rate of about 107 K/second in order to make the alloy amorphous to obtain the improvement effects. Thus, a materials thickness for production is limited to a very small value, so that it is considerably difficult to produce a material having a thickness of about 30 xcexcm.
Further, according to a result that the present inventors examined an amorphous metal on the basis of the above mentioned chemical composition in various points of view, the material having a thickness of about not less than 30 xcexcm did not become completely amorphous, and there occurred deterioration of corrosion resistance and brittleness because a lot of precipitates, each of which had a diameter of about not less than 0.1 xcexcm and which were carbides, borides, etc., was generated in the metal structure. The precipitates were mainly carbides including M7C3 and M23C6 and borides including Fe3B, Fe2B, Cr3b and Cr2B.
An object of the present invention is to provide a razor blade material which has excellent corrosion and wear resistances and contains a reduced amount of precipitates, and which can ensures a cutting edge form of a razor blade made thereof to have a good accuracy and excellent sharpness. More particularly, the object is to provide the razor blade material which is made to an amorphous metal structure containing a reduced amount of precipitates and which can have a large thickness and a high hardness of a cutting edge portion. Another object of the present invention is to provide a razor blade made of the razor blade material.
The present inventors intensively studied chemical compositions and microstructures of some variances of the razor blade material. As a result, it has been found that there is a state of precipitates effective for improvement of corrosion resistance and inhibiting brittleness, and that there is a chemical composition range in which alloying elements of C, Cr and Mo are adjusted to have optimized contents, respectively, so as to inhibit formation of precipitates. Further, some alloying elements have been identified, and it has been found also that an appropriate amount of B and Si can be effectively added into the material. The inventors examined also an amorphous structure advantageous for inhibiting formation of precipitates. As a result, the present invention has been achieved.
According to a first aspect of the present invention, there is provided a razor blade material made of an Fe-base alloy comprising, by mass %, not less than 0.5% carbon, 9.0 to 14.0% Cr and from more than zero to 8.0% Mo, wherein precipitates, which can be observed at an optional cross section of the razor blade material, have a diameter of less than 0.1 xcexcm, respectively.
According to a second aspect of the present invention, there is provided a razor blade material made of an Fe-base alloy consisting essentially of, by mass %, not less than 0.5% carbon, 9.0 to 14.0% Cr and from more than zero to 8.0% Mo, B and/or Si in an amount as defined by the equation of 0 less than B+Sixe2x89xa68.0%, and the balance of Fe and unavoidable impurities, wherein precipitates, which can be observed at an optional cross section of the razor blade material, have a diameter of less than 0.1 xcexcm, respectively. The razor blade material has high hardness, high strength and good corrosion resistance.
According to a third aspect of the present invention, there is provided a razor blade material made of an Fe-base alloy comprising, by mass %, not less than 0.5% carbon, 9.0 to 14.0% Cr and from more than zero to 8.0% Mo, wherein no precipitate can be observed at an optional cross section of the razor blade material.
According to a fourth aspect of the present invention, there is provided a razor blade material made of an Fe-base alloy consisting essentially of, by mass %, not less than 0.5% carbon, 9.0 to 14.0% Cr and from more than zero to 8.0% Mo, B and/or Si in an amount as defined by the equation of 0 less than B+Sixe2x89xa68.0%, and the balance of Fe and unavoidable impurities, wherein no precipitate can be observed at an optional cross section of the razor blade material.
Preferably, a metal structure of the razor blade material includes an amorphous structure in a volume fraction of not less than 30 volume %. Thereby, the corrosion resistance and mechanical properties are greatly improved. Herein, the term of xe2x80x9camorphous structurexe2x80x9d may include also a grain boundary layer which is a kind of amorphous structure.
Further preferably, the razor blade material of the present invention has a thickness of 30 to 100 xcexcm.
Further, preferably, the razor blade material of the present invention may be coated with polytetrafluoroethylene (PTFE). This improves a feeling during shaving.
A key aspect of the invention resides in that the razor blade material can be of a small content of fine precipitates by virtue of an adjusted optimum chemical composition. More particularly, according to the razor blade material, precipitates each having a diameter of not less than 0.1 xcexcm can not be observed at an optional cross section thereof. In order to obtain the alloy structure of the invention, for example, it is effective to use a quenching solidification method according to which a thick amorphous material, particularly including an amorphous structure in a volume fraction of not less than 30 volume %, can be produced even if a solidification rate is at a critical cooling rate of about 5xc3x97104 K/second. Therefore, the above mentioned state of precipitates can be advantageously achieved, and the invention razor blade material can be realized as solidified by quenching.
First, a structure control will be described as a principle of the invention. The invention razor blade material is adjusted to have a small content of fine precipitates in order to obtain high hardness, high strength and good corrosion resistance. It is an efficient way for such an adjustment to make the material to have an amorphous structure.
In order to obtain such a metal structure according to the invention, a matrix of the material is controlled to become a nanocrystalline structure, an amorphous structure containing a dispersed nanocrystalline structure or an amorphous structure. FIGS. 1A to 1C show schematic illustrations of typical microstructures of the invention. When the matrix is the nanocrystalline structure (see FIG. 1A), a carbide precipitation is inhibited because the volume of a grain boundary layer as a kind of amorphous structure increases whereby a solid-soluble limit of solute elements in the grain boundary layer increases. For example, a usual industrial product of razor blade materials has a grain size of about 10 xcexcm, and contains the grain boundary layer in a volume fraction of about 0.02%. On the other hand, if the nanocrystalline structure has a grain size of about 10 nm, its grain boundary layer has a volume fraction of about 20%, so that the solid-soluble limit of solute elements increases by about 1000 times.
Moreover, when the matrix has the amorphous structure containing dispersed grains of the nanocrystalline structure (see FIG. 1B), it is hard to be a site of precipitation, because, in addition to the above effect in the case of the nanocrystalline structure, an interface between the nanocrystalline structure and an amorphous structure has a low interface energy like as an interface between a solidus and liquidus, and has a closed-packed atomic arrangement without excess voids. In the case where a matrix has an amorphous structure (see FIG. 1C), it will be needless to say that formation of precipitates is effectively inhibited. Thus, it is possible to inhibit formation of precipitates in such an adjusted alloy structure, where by providing the alloy material with a combination of high hardness, high strength and good corrosion resistance.
According to the above described technique, no precipitate can be observed in the metal structure of the invention razor blade material, or the metal structure contains precipitates each having a diameter of less than 0.1 xcexcm, and the invention material has a metal structure without crystal grain boundaries which usual crystalline metals have, because it is controlled to have the nanocrystalline structure, the amorphous structure containing dispersed grains of the nanocrystalline structure or the amorphous structure. Therefore, a cutting edge region can be finished to be smoother when forming a cutting edge in a finishing process of razor blades, and sharpness during use of the razor blade is also remarkably improved.
Herein below, there will be provided a description of the component elements of the invention razor blade material and a reason why contents of alloying elements are limited to given amounts, respectively.
(a) C: not less than 0.5%
Carbon is an element necessary for improving strength of the material. A much carbon content lowers the melting point of the material and improves productivity of the same. Thus, the carbon content is set to be not less than 0.5%. Preferably, the carbon content is not more than 5.0% in order to inhibit crystallization of graphite.
(b) Cr: 9.0 to 14.0%
Cr is a basic element necessary for providing the material with corrosion resistance, and required to be not less than 9.0% Cr in order to ensure substantially the same level corrosion resistance as that of stainless steel. However, a Cr content exceeding 14.0% makes the material not only expensive but also susceptible to crystallize coarse network carbides resulting in deteriorated hot-workability and a low productivity. In order to prevent the crystallization of carbides, quick quenching is necessary for the material. Therefore, the Cr content is set to be 9.0 to 14.0%.
(c) Mo: not more than 8.0%
Mo improves corrosion resistance. Mo is effective for not only preventing coarsening of Cr-containing carbides but also preventing precipitation of other carbides, since it occupies precipitation sites of Cr-containing carbides (M7C3 or M23C6) susceptible to be coarse and is effective for lowering a diffusion activity of carbon because of a high affinity for carbon. However, when the Mo content is much, a brittle phase precipitates to deteriorate the material in corrosion resistance and toughness, the brittle phase comprising a lot of Mo-containing carbides (including Mo2C) and composite borides (including Mo2(Fe, Cr)B2, Fe13Mo2B5, Mo3B and Mo2B). Thus, an upper limit value is set to be 8.0%. Preferably, the Mo content is not less than 0.5% in order to obtain the above effects.
While the invention material is directed to an Fe-base alloy containing the above components with specific contents, respectively, it is effective for the material to contain B (boron) and Si in order to further improve characteristics of the material.
(d) B+Si: not more than 8.0%
Both elements B and Si promote a transformation of a alloy structure of the material into amorphous. However, a much amount of the elements prevents such a structural transformation and causes a lot of brittle phase to precipitate resulting in deteriorated toughness, the brittle phase comprising composite borides (including Mo2(Fe, Cr)B2, Fe13Mo2B5, Mo3B and Mo2B), Fe3Si and Fe2Si. Thus, in the present invention, an upper limit of a total content of one or both of the elements is set to be 8.0%. Preferably, the content thereof is not less than 0.5% in order to obtain the above effects.
It should be also noted that other elements promoting the structural transformation into amorphous can be added into the material as long as basic actions by the above chemical composition and a microstructure described below are not deteriorated. Such elements may be P, Nb, Zr, Ta, Al, Ga, Ni, Co and Cu.
(e) Precipitates observed at an optional cross section of the material and having a diameter of less than 0.1 xcexcm (including a case where no precipitate can be observed). The precipitates can improve the material in strength, toughness and wear resistance. However, precipitates having a large size not only deteriorate the toughness but also deteriorate the corrosion resistance because the precipitates deprive Cr and Mo from the matrix while they are effective for improving the corrosion resistance. Therefore, it is important to form an alloy structure in which no precipitates each having a diameter of not less than 0.1 xcexcm can be observed in order to provide the material with a combination of good alloy properties of strength, toughness, wear resistance and corrosion resistance.
In order to confirm a state of precipitates in the invention material, an alloy structure may be observed by means of a scanning electron microscope or a transmission electron microscope. In the case of the scanning electron microscope, a specimen is produced by electrolytic polishing (including the speed process), and it can be observed at an acceleration voltage of 5 to 15 kV and a magnification of up to 100,000. In the case of the transmission electron microscope, a specimen is produced by ion milling, and it can be observed at an acceleration voltage of 200 kV and a magnification of up to 300,000. The size of precipitates may be determined by converting a maximum diameter of precipitates, obtained by conducting an image processing with utilization of 20 photographs taken at a magnification according to which not less than 20 precipitates are present in one view field, into a corresponding circle diameter.
(f) Amorphous in the alloy structure: a volume fraction of not less than 30%
The amorphous structure remarkably improves corrosion resistance and strength of the material. Further, if a grain boundary layer as a kind of amorphous structure increases, it is possible to inhibit the above carbides, composite borides and so on from precipitating because a solid-soluble limit of solute elements in the grain boundary layer increases. Therefore, a volume fraction of the amorphous structure is preferably not less than 30%, more preferably not less than 50% and desirably not less than 70%.
In order to confirm the volume fraction of the amorphous structure in the invention material, it is possible to conduct, for example, a structural observation by means of a transmission electron microscope, and an analysis by means of an electron beam diffraction and an X-ray diffraction. As one example, first an X-ray diffraction process is conducted, and subsequently the structural observation by means of the transmission electron microscope or the analysis by means of the electron beam diffraction is conducted. The transmission electron microscope observation is conducted under the above mentioned conditions, and the electron beam diffraction may be conducted by a limited view field diffraction method.
Further, the volume fraction of the amorphous structure may be determined as follows.
If the whole matrix is an amorphous structure (see FIG. 1C), it can be confirmed by all the above mentioned methods. If the matrix consists of an amorphous structure and a nanocrystalline structure dispersed in the amorphous structure (see FIG. 1B), the volume fraction of the amorphous structure can be obtained by determining the volume fraction of the dispersed nanocrystalline structure by means of an observation with utilization of a transmission electron microscope and an image analysis, thereafter calculating the volume fraction of the amorphous structure by subtracting the volume fraction of the nanocrystalline structure from the total volume. If the matrix consists of a nano-crystal structure (FIG. 1A), the volume fraction of the nano-crystal structure can be obtained by determining a grain size of the nanocrystalline structure (*Note: the cutting method such as rhombic dodecahedron approximation is used for the determination) by means of an observation with utilization of a transmission electron microscope, and thereafter a volume of a grain boundary layer may be calculated on the basis of the determined grain size and a generally agreed grain boundary thickness (assumed to be about 1 nm).
(g) Thickness of 30 to 100 xcexcm
One feature of the invention razor blade material is that it can have a thickness of not less than 30 xcexcm. Thereby, it is possible to minimize or omit the post-casting process steps of hot-working, cold-working, heat treatment and so on, whereby production process steps can be notably saved. For example, in the case where the invention razor blade material is produced by the quenching solidification method, it can be used as solidified by quenching.
(h) Coating with polytetrafluoroethylene (PTFE)
The invention razor blade material is characterized by that it may be used with a coat of polytetrafluoroethylene (PTFE). Thereby, a shaving feel, which is one of important properties of the razor blade, can remarkably improved.
As mentioned above, it is effective to use the quenching solidification method in order to obtain the invention razor blade material. In this case, when the solidification rate is a level of critical cooling rate of 5xc3x97104 K/second, the invention razor blade material may be as solidified by quenching, and it is possible to attain the blade material having a thickness of not less than 30 xcexcm. However, it should be noted that an excess thickness is inappropriate in order to attain the amorphous structure, and that the upper limit of thickness of the material as solidified by quenching, which is attainable at the cooling rate mentioned above, is an order of 100 xcexcm. Therefore, the thickness of the invention material is set to be a range of 30 to 100 xcexcm.
According to the chemical composition of the invention material, as described above, although it is of a component system according to which comparatively large precipitates including carbides are generated when the material is produced by a usual melting and casting method, it is possible to minimize precipitates by applying a producing method such as the quenching solidification method. In this case, even if the solidification rate is a level of critical cooling rate of 5xc3x97104 K/second, it is possible to attain a metal structure in which no precipitate having a diameter of not less than 0.1 xcexcm can be observed at an optional cross section of the material. Thus, it is possible to produce a blade material having a larger thickness than the conventional material. Thereby, the invention material is advantageously used for a razor blade material such that, when a razor blade is made from the material, a cutting edge portion thereof has a high hardness, a good accuracy of the edge form, an excellent sharpness, and excellent properties of corrosion resistance and wear resistance.
Additionally, it is possible to raise some examples of the manufacturing method of the invention blade material having the structure in which no precipitate having a diameter of not less than 0.1 xcexcm can be observed. They are a casting method using a copper mold, a suction casting method and a molten metal forging method according to which the solidification rate corresponding to the critical cooling rate of 5xc3x97104 K/s can be obtained, a liquid quenching method (e.g. a single roll method) according to which quick-quenching is possible, a gas phase condensation method (e.g. an electron beam vapor deposition method), a solid phase reaction method (e.g. mechanical alloying), a chemical reduction method (e.g. a plating method), and so on.
According to the invention razor blade material, the amorphous structure having a volume fraction of not less than 30 volume % is hardly transformed even under a usual heat treatment condition (i.e. a heating rate of about 0.6xc2x0 C./s) for coating the material with polytetrafluoroethylene (PTFE), and a sufficient effect can be expected in the case of rapid heating at not less than 80xc2x0 C./s.
As described above, according to the present invention, it is possible to provide the material which has a comparatively large thickness, high hardness, high strength and high corrosion resistance. Thus, it is just suitable for a razor blade material. The invention material can be applied to other cutlery as well as razors.
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